A requirement for internal combustion engines, particularly diesel engines is that the limit values of nitrogen oxide emission be respected, wherein decreasing legal limit values requires a reduction of said nitrogen oxide emissions. One possibility of reducing nitrogen oxide emissions is to recycle portions of an exhaust gas into the combustion chamber, which makes it possible to set an oxygen concentration in the combustion chamber of the cylinder. This so-called exhaust gas recirculation, (EGR) represents the possibility of reducing the oxygen concentration in the combustion chamber of the cylinder. For this purpose, the precise setting of the oxygen concentration in the cylinder is of central importance during a transient or stationary operation. While a stationary operation of an internal combustion engine does not entail more stringent requirements in terms of adjustment control, an exhaust gas recirculation must be determined as precisely as possible during transient operation to be able to represent a good correlation of the nitrogen oxide emission. In exhaust gas recirculation, a distinction is made between internal and external exhaust gas recirculation. Internal exhaust gas recirculation consists of the return flow of exhaust gas out of the outlet channel into the combustion chamber during a valve overlapping phase. Here, the level of the internal exhaust gas recirculation depends on a pressure difference between fresh air feed and the exhaust gas system, the duration of valve overlapping, and the opening cross sections cleared by the valves. By a targeted variation of the valve overlapping, the internal exhaust gas recirculation can be optimized for the given load and operating conditions. For example, if it is possible to influence the valve lifting by means of a phase adjuster, then the internal exhaust gas recirculation becomes adjustable. Another known exhaust gas recirculation consists of external exhaust gas recirculation. Here, high-pressure exhaust gas recirculation, which allows a direct recirculation of the exhaust gases in the area of the exhaust gas manifold into the fresh air feed of the inlet channel, is distinguished from low-pressure exhaust gas recirculation, wherein the exhaust gas is diverted behind a turbine integrated in the exhaust gas system, and fed to the fresh air feed even before the charging.
One possibility for controlling the internal exhaust gas recirculation is described in DE 34 01 362 A1. A variable valve control method is described, whereby the inflow and outflow of the work medium can be controlled. Such a flexible control offers the advantage that, during stationary operation of the internal combustion engine, the feed of the work medium can be adjusted to the different operating states. As a result of an appropriate control of the inlet and outlet valves, the exhaust gas quantity in the cylinder is increased, so that the remaining cylinder volume is lowered to suction fresh mixture. Due to the lower suctioned fresh mixture quantity, the load is reduced. This procedure can be considered up to approximately half the maximum load. A further lowering of the load can be achieved by reducing the exhaust gas quantity remaining in the combustion chamber from the previous work cycle, by means of appropriate control times of the inlet and outlet valves at the upper dead point, and also due to the reduction of the fresh air quantity reaching the combustion chamber, by means of appropriate control times for the inlet valve. Using a variable valve timing, (VVT), a possibility is provided for adjusting an internal exhaust gas recirculation. The content of this printed document in relation to VVT is included here in its entirety in the disclosure of the invention.
An adjustment control to minimize a nitrogen oxide emission in the exhaust gas of an internal combustion engine is disclosed in WO 2008/131788. A method is disclosed in which to set nitrogen oxide emissions where nitrogen oxide values in the exhaust gas of the internal combustion engine are monitored and set in correlation with a nitrogen oxide limit value, and the combustion adjustment control, on the basis of values of the nitrogen oxide adjustment control, carries out an adaptation of the nitrogen oxide adjustment control, for the purpose of respecting the nitrogen oxide limit value. Besides virtual values of an air consumption, an exhaust gas recycle rate, and an oxygen quantity proportion, measured quantities, as well as quantities taken from characteristics fields of a substance, quantitative proportion of nitrogen oxides are also incorporated in the calculation of a particle concentration in the exhaust gas and of a virtual substance quantitative proportion of nitrogen oxides in the exhaust gas. To determine the nitrogen oxide proportions in the exhaust gas, a nitrogen oxide sensor is used, whose determined value is used in an adjustment control unit for the adjustment control of an exhaust gas recycle valve. The disclosure of this printed document is also included in its entirety in the disclosure of the invention, particularly with regard to the external exhaust gas recirculation as well as the modeling.
An additional possibility of influencing the nitrogen oxide proportions in the exhaust gas of an internal combustion engine is disclosed in WO 2008/131789. An adjustment control system is disclosed for regulating the exhaust gas recycle rate by means of a virtual nitrogen oxide sensor with an adaptation via a nitrogen oxide sensor. To take into account a delay by means of a nitrogen oxide sensor, a first adjustment control means, which simulates a virtual nitrogen oxide sensor, a second adjustment control means carries out an adaptated adjustment control of the virtual nitrogen oxide sensor, and a third adjustment control agent implements the nitrogen oxide adjustment control, wherein the first adjustment control is constructed in such a manner that the virtual nitrogen oxide sensor establishes a presetting for the first adjustment control. Due to the disclosed method, an adjustment control of an exhaust gas recirculation mass flow becomes possible, where using an exhaust gas recirculation mass flow as adjustment control variable is preferred. By setting the exhaust gas recirculation mass flow, an oxygen content in the suction pipe of the internal combustion engine is set. A virtual nitrogen oxide sensor analyzes a virtual oxygen content, which is corrected by an adapted value, thus allowing the derivation of a virtual nitrogen oxide value in the exhaust gas. Besides the known acquisition and calculation alone of a nitrogen oxide value, a temporal delay in the acquisition of a nitrogen oxide sensor is taken into account by means of a model-based calculation of a nitrogen oxide value. This printed document is also included in its entirety in the disclosure of the invention, particularly with regard to the modeling and adjustment control.
The problem of the invention is to make possible an improved exhaust gas behavior of an internal combustion engine over an operating range, wherein a rapid adjustment control is made possible.